Effect of adaptogens on muscle tissue microstructure of hybrid pigs (Sus scrofa domesticus L.) during intensive fattening

At present, improving the quality of pork while increasing the production of pork is of generally recognized economic importance. Diets have been shown to affect the characteristics of muscle fibers. Adaptogens (vitamins and bioflavonoids) that animals need during active growth period can prevent myopathic transformation in meat. This paper for the first time reports on the improved microstructure of the musculus longissimus dorsi in crossbred pigs fed a complex of adaptogens (dihydroquercetin and vitamins E, C) during the fattening period. Our aim was to evaluate the effect of the complex of dihydroquercetin + vitamins E, C on the microstructure of meat muscle tissue in hybrid pigs. The experiments were carried out in 2021-2022 at Gorbatov Federal Research Center of Food Systems, Ernst Federal Research Center for Animal Husbandry and BMPK (Bryansk Province). Crossbred piglets ( n = 108) ( Sus scrofa domesticus ) F2 [(Large White ½ Landrace) ½ Duroc] were randomly selected and assigned to two groups, n = 54 each, for a 58-day fattening. The control group were fed only a complex feed (SK-6, Russia), The test group was additionally fed an experimental dietary complex of adaptogens (DEC) that contains dihydroquercetin (DHQ, Ecostimul-2, JSC Ametis, Russia; 72-73 % DHQ, 32 mg/kg of feed), vitamin E (INNOVIT E60, GC MEGAMIX, Russia; 10 mg/kg feed) and vitamin C (Tiger C 35, Anhui Tiger Biotech Co. Ltd., China; 35 mg/kg feed). Young animals were weighed twice (on day 0 and day 58) by group weighing and individual weighing of 10 animals from each group. After slaughter, the paired carcass weight and the slaughter yield were assessed. To study the microstructure of muscle tissue, 45 min after slaughter, samples (3½3½3 cm) of the longest back muscle ( musculus longissimus dorsi ) were collected and fixed in 10 % neutral buffered formalin solution for 72 h at room temperature. For further study, two fragments (1.5½1.5½0.5 cm) of each sample with longitudinal and transverse orientations were washed with cold running water for 4 h, then compacted at 37 °C in gelatin (AppliChem GmbH, Germany) of ascending concentrations (12.5 and 25 %, for 8 h in each). Serial 16 µm sections were prepared using a MIKROM-HM525 cryostat (Thermo Scientific, USA), mounted on Menzel-Glaser glasses (Thermo Scientific, USA) and stained with Ehrlich’s hematoxylin and 1 % eosin water-alcohol solution (BioVitrum, Russia). The histological preparations were examined and photographed using an AxioImaiger A1 light microscope (Carl Zeiss, Germany) with a connected AxioCam MRc 5 video camera (Carl Zeiss, Germany). Morphometric studies were performed using the AxioVision 4.7.1.0 image analysis program (Carl Zeiss, Germany). Muscle fiber diameter, sarcomere length, and giant fiber cross-sectional area were measured online. On cross sections, the shape of muscle fibers, their density, the state of the nuclei, the thickness and state of the connective tissue layers were investigated, and giant fibers were identified. On longitudinal sections, the state and shape of muscle fibers, the state of the sarcolemma, the presence of striation (transverse, longitudinal) and destructive changes (ruptures, cracks, fragmentation), hypercontraction nodes were identified. Despite the absence of statistically significant differences in live weight and slaughter traits between groups during fattening, histological studies revealed significant differences in average values of muscle fiber density (p = 0.02) and sarcomere length (p = 0.000007). Almost a 2-fold decrease in the number of giant fibers in test group (11.60 vs. 21.30 pcs/cm2) indicates a significant improvement in the tissue microstructure compared to the control animals that did not receive DEC. The less pronounced destructive changes in the sarcolemma in the test animals also indicate an increase in the animal stress resistance. Given a significant variability of morphometric parameters in both groups, we applied a scoring procedure which allows us to classify carcasses according to the severity of myopathic changes in muscle tissues based on the results of the muscle fiber microstructure study. In control, there was only one carcass that had no signs of myopathy; four carcasses showed signs of moderate myopathy and five carcasses showed signs of severe myopathy. On the contrary, in the test group, there were four carcasses without signs of myopathy and six carcasses with signs of moderate myopathy. There were no cases of severe myopathy in the study group. The groups differed statistically significantly (p = 0.004) in scores characterizing the severity of myopathic changes in muscle tissue. Our findings show that the dietary adaptogen complex DEC can provide the improvement of the microstructure of the muscle tissue and, therefore, has a positive effect on animal stress resistance and the degree of glycolysis in meat.